Conventionally, stamping (i.e., displaying or printing) of date and time (hereinafter referred to as “time” as a generic term for date and time) of production on a product is done in order to specify when the product was produced. Simply stamping time on a product, however, is not enough to prove whether it is true or not that the product was produced at the time stamped thereon.
As a solution to this problem, Patent Document 1 proposes a system and method for certifying the authenticity of stamped time. According to this document, time and temporal change information specified by the time (e.g., weather information released at the time) are combined to generate combined information. The combined information is then stamped on a product. Stamped combined information makes it possible to certify the date and time of production of the product at a later time.
Patent Document 1: Unexamined Patent Publication No. 2001-297062